During aging, organisms show altered gene expression patterns and have an increasingly impaired ability to respond to stress-causing and mitogenic stimuli. Since post-transcriptional processes critically regulate changes in the collections of expressed proteins, it is extremely important to elucidate the microRNAs (as well as RBPs, as described in other projects) that control age-related gene expression patterns. To investigate microRNA function during senescence, we employ approaches such as microRNA reduction (by transfecting an antisense RNA), microRNA overexpression (by transfecting a precursor of the microRNA), and the identification of microRNA-associated mRNAs by transfecting biotinylated microRNAs and identifying target mRNAs through various methods (eg, microarray, RT-PCR). We investigate whether microRNAs affect the stability of target mRNAs during senescence by measuring the steady-state levels and half-lives of the mRNAs of interest as a function of microRNA abundance. We investigate whether microRNAs affect the translation of target mRNAs by modulating microRNA levels, and subsequently studying the relative assocation of the mRNA with translating polysomes and by quantifying the nascent translation rates of the encoded proteins. We also employ reporter constructs to gain additional insight into the processes modulated by microRNAs and use different senescence-associated markers to examine changes in the senescence phenotype. During the past funding period, we have reported that in human diploid fibroblasts the microRNA miR-519 plays a central role in the implementation of replicative senescence (Marasa et al., Aging, 2010). We also discovered that miR-519 triggers senescence at least in part by lowering expression levels of the RBP HuR (Abdelmohsen et al., Cell Cycle, 2010). We also participated in collaborative efforts with the Evans laboratory to identify differences in microRNA expression patterns as a function of age (Noren et al., PLoS ONE, 2010). Ongoing studies are analyzing systematically the target mRNAs of biotinylated microRNAs whose levels decline or increase with senescence. There is also a great deal of interest in elucidating other noncoding RNA with roles in cellular senescence and aging.